Population dynamics of Paratylenchus nanus in soil under pasture: 1. Aggregation and abiotic factors

Paratylenchus nanus populations were assessed by seasonal and monthly sampl ing of grazed pasture on silt loam soil in Waikato, New Zealand. The data w ere used to investigate P. nanus aggregation and relationships with abiotic factors, including soil temperature, rainfall, soil moisture and soil nutr ients. P. nanus was more abundant at 10-20 than 0-10 cm soil depth and popu lations were greatest in summer. Aggregation declined from spring through t o winter. P. nanus populations were positively correlated with soil tempera ture and negatively with soil moisture (seasonally) and rainfall (monthly). Monthly P. nanus abundance was also positively correlated with a combinati on of accumulated temperature and rainfall. On single occasions, soil phosp horus and nitrogen were significantly negatively correlated with P. nanus p opulations, and it is suggested that these associations were mediated throu gh host plant abundance.